AR coating is widely used in image sensors. It is generally applied on top of a cover glass or a lens, and is situated with its air interface facing incoming light. As shown in FIG. 9, a packaged complementary metal oxide semiconductor (CMOS) image sensor package 900 includes a cover glass 910, a CMOS image sensor (CIS) device 930 that comprises microlens (not shown), substrate, photo detection regions (not shown), and metal connect regions (not shown), dams 940, and solder balls 950. The top of the cover glass 910 is coated with an AR coating 920, which is situated with its air interface facing incoming light.
One type of AR coating is a multi-layer coating, consisting of multiple layers of high and low refractive index materials. Based on the principle of destructive interference, the multi-layer AR coating works to reduce light reflection to be within only a few percent of incoming light, so that optical transmission is enhanced.